Third-order Stream Research Articles

Shaping the future of conservation: a model for restoring oxbows in Iowa and beyond

Oxbows, once an abundant and natural feature of the landscape, have been nearly eliminated due to the effects of the Anthropocene, consequently impacting water quality, flood storage capacity, and the wildlife that depend on this habitat. These depressional basins within floodplains naturally accumulate sediment over time, but the sedimentation rate of oxbows over the last 100 years has greatly increased. The primary sources of sediment are from human activity, including erosion from agricultural fields and urban developments, drainage alterations, precipitation changes associated with climate change, and disconnection from their rivers and natural river hydraulics. Outlined in this manuscript is a step-by-step guide for restoring oxbows, based on 20 years of experience and lessons learned implementing oxbow restorations in Iowa on first-, second-, and third-order streams. Our goal is to provide conservation services providers and others interested in restoring degraded oxbows with the tools and expertise to confidently restore oxbows to achieve conservation goals.

Land use characteristics affect the sub-basinal scale urban fish community identified by environmental DNA metabarcoding

The heterogeneity of urban landscapes has effects on the environmental characteristics and fish composition of individual urban streams, even within a single water system. It is, therefore, imperative to assess the influence of physiochemical properties on urban streams by analyzing the spatial distribution of fish communities at the local scale. However, conventional fish surveys encounter time and labor constraints when selecting and surveying dense sampling points under 2 km in stream networks. In this study, environmental DNA (eDNA) metabarcoding was used as an innovative survey methodology to identify the effects of land use and stream order on fish composition and tolerance guild in an urban area. The eDNA sampling was conducted in 31 sites of the Anyang stream network in Korea, including part of the stream undergoing ecological restoration. The eDNA survey detected 12 of 17 species (70.6%) that appeared in the historical data, and 12 of 18 species (66.7%) identified in a conventional field survey with kick nets and casting nets. The proportions of urban area, forest and grassland were positively correlated with abundance (p < 0.05) and richness (p < 0.05) in multiple regression analyses, while the proportion of agricultural area showed a negative correlation (p < 0.05). For abundance, richness, and diversity within the fish community from first- to third-order streams, there was a significant decrease in sensitive species (p < 0.05) alongside a significant increase in tolerant species (p < 0.01) across all three indices. The results of this study highlight variations in fish composition across sites within the local scale of the urban stream network, underscoring the need for detailed monitoring to understand the ecological function of urban streams.

Landscape regulation of microbial use of terrestrial carbon in boreal streams

Microbes decomposing leaf litter in aquatic ecosystems are exposed to two major sources of carbon (C), namely, particulate organic C (POC) and dissolved organic C (DOC). The use of DOC relative to POC during litter decomposition likely depends on the availability of DOC, which in turn is regulated by the characteristics of the surrounding landscape, although this extrinsic indirect control of DOC use remains largely unexplored. We have investigated how variations in stream physical and chemical characteristics, distribution of major landscape elements (i.e., forest, mires, and lakes), and riparian vegetation community composition (i.e., relative cover of deciduous vs. coniferous tree species) influence DOC use by leaf-associated microbes (LAM). Specifically, in a boreal stream network of ten first- to third-order streams, we related in-stream characteristics, landscape elements, and riparian vegetation community composition to DOC/POC respiration ratios (i.e., the amount of CO2 produced by LAM respiration of DOC + POC divided by the amount of leaf C mass lost through decomposition). The results showed that DOC/POC respiration ratios were > 1 in most of the study sites, indicating that LAM use a substantial amount of DOC during leaf litter decomposition. This microbial reliance on DOC varied with in-stream DOC and nutrient concentrations, proportional mire and forest cover, and riparian vegetation community composition. In particular, high mire and coniferous cover increased DOC use by LAM. As such, landscape configuration and how it is modified by land use and climate change must be considered in order to understand microbial turnover of terrestrial C in boreal streams.

The theory of fifth-order Stokes waves in a linear shear current

In this study, a new set of fifth-order Stokes wave solutions, incorporating the effects of a linear shear current, is derived by using the perturbation method originally proposed for pure waves that was recently published. The present solutions are checked against the existing experimental data, the third-order stream function solutions, as well as the numerical results. The comparisons demonstrate that the present solutions are more accurate in describing the velocity distributions during wave propagation, especially in strong following currents and negative vorticity conditions. Subsequently, the present solutions are used to investigate the fluid particle trajectories for different wave–current interaction conditions. The results indicate that the background vorticity can alter the patterns of fluid particle trajectories and the direction of Stokes drifts.

An Assessment of Streambank Erosion Rates in Iowa

Streambank erosion is a major contributor to watershed suspended sediments and phosphorus exports in many regions, but in Iowa and other midwestern states, the load contribution from streambanks is not considered by state nutrient reduction strategies. The study’s objectives were to evaluate the annual bank erosion rates measured in Iowa using erosion pins and aerial imagery and assess how recession rates vary across space, time, and stream order. The overall goal was to determine whether there are global similarities to these streambank recession rates that could be generalized and scaled up for regional assessments using data from Iowa-based erosion pin studies and original research on stream migration rates. At the erosion pin sites, the recession rates averaged approximately 11 cm yr−1 in third-order streams and, when combined with stream migration analyses, we observed scaling associated with bank recession rates at longer time scales across a range of stream orders. More bank recession occurs in larger streams and rivers with greater discharge from larger watershed areas and an increase in stream power. Variations in these bank recession rates were observed in Iowa landform regions mainly due to differences in geology and the composition of the streambank sediments. The study’s results provide a temporal and spatial context for evaluating streambank recession in Iowa and the glaciated Midwest.

Catchment-scale deer exclusion changes longitudinal patterns of macroinvertebrate communities through soil runoff mitigation

Deer overpopulation is occurring worldwide, and deer-induced soil runoff into streams increases levels of suspended sediment and fine sedimentation. While deer-induced fine sedimentation in depositional habitats including first- and fourth-order streams is known to alter macroinvertebrate communities, effects of drifting suspended sediment in erosional habitats between the stream orders are poorly understood. Here, habitat and macroinvertebrate community structures in first- to third-order streams were compared between deer-excluded and grazed catchments of a Japanese headwater system. Fine sediment cover on the streambed was significantly greater in the grazed catchments than the deer-excluded catchment only for first-order streams, while macroinvertebrate community structure differed distinctly between the deer-excluded and grazed catchments at all stream orders. Burrowing collector-gatherers, which inhabit fine streambed sediments, were less abundant in first-order streams in the deer-excluded catchment than the grazed catchments, while clinging collector-filterers, which are vulnerable to suspended sediment inputs, were more abundant in second- and third-order streams of the deer-excluded catchment than the grazed catchments. These results suggest that the effect of deer exclusion on stream ecosystems varies with longitudinal changes in sediment deposition and transport capacity. Hydro-geomorphological processes are thus fundamental to assessing the restoration of forest-stream ecosystems, particularly in spatiotemporally dynamic headwater systems.

Visual Harmony of the Proportion of Water and Greenery in Urban Streams: Baxi Stream, Yongan City, China

This study investigated the visual harmony of an urban stream considering changes to the ratio of water to greenery on the riverbed. The Baxi stream, a third-order stream in Yongan City, Fujian Province, China was selected as the study site. The stream reach is disturbed by several hydraulic structures, such as restricted water flow by a vertical revetment and water level regulation by submerged dams. Images of the river were captured, and image processing was performed to change the proportion of water and greenery, and the proportions of various landscape elements in the image were calculated. Based on the statistical analysis of survey results, cognitive indicators (vividness and naturalness) associated with harmony and preference, and the relationship between harmony or preference and landscape elements, were established. Landscape elements included ratios of visible water (WR), visible greenery (GR), visible buildings, and visible infrastructure. The results demonstrated that visual preference, P, is positively correlated with harmony, H, vividness, V, and naturalness, N. In particular, H is almost consistent to P. The proportion of visible water and greenery had a significant impact on the H and P of the stream landscape. When the ratio of WR to GR was approximately 0.8, H was optimal, and the public’s P was high. These results can be used to improve and enhance the visual landscape quality of this stream reach. The methodology proposed in this study could provide other study areas with a reference for how to obtain the best visual harmony or achieve public acceptance by changing the amount of visible water and/or greenery.

Organic litter dynamics in headwater streams draining contrasting land uses

Climate change could alter fluxes of organic matter and macronutrients through freshwater ecosystems potentially affecting stream organisms. However, riparian controls on litter dynamics offer an opportunity to adapt headwaters to climate change by protecting or restoring riparian vegetation. We assessed how riparian land cover and climatic variability affected the supply, retention and downstream transport of particulate organic matter (POM) in headwaters—the most extensive small water bodies in temperate landscapes. Leaf litter inputs, benthic stocks and suspended organic matter were measured nominally monthly in second–third-order streams draining broadleaf woodland, conifer, acid moorland and circumneutral moorland over four years with varying discharge. Streams draining broadleaf woodland received more leaf litter from the riparian zone than conifer and moorland and transported higher concentrations of CPOM and FPOM at base flows. Broadleaf sites had higher CPOM stocks, even after hydrological events that reduced CPOM in conifer and moorland sites. In contrast, FPOM dynamics reflected hydrological conditions irrespective of land cover. These results show how some organic matter fractions in streams are sensitive to hydrological conditions, illustrating how wetter climates will influence FPOM exports. Nevertheless, riparian broadleaves have the potential to offset climatic effects on organic matter processing in headwaters through the replenishment and retention of CPOM.

Fine-Grained Sediment and Phosphorus Storage in a Suspended-Load-Dominated, Alluvial Channel

HighlightsIn-channel sediment and TP storage were quantified along 13.5 km of a stream.TP and sediment masses were 1 and 3 times greater than their respective annual watershed load.Colluvial material at streambank toe represented the dominant storage pool.Sinuous stream reaches exhibited significantly greater storage versus channelized reaches.Abstract. In-channel storage of both fine sediment and sediment-bound phosphorus has been recognized as potentially large contributors to respective watershed loads, yet they are rarely quantified in the field. In this field-based study, we quantified and characterized in-channel fine sediment and total phosphorus (TP) storage within a third-order stream. We hypothesized storage to be significant within the context of watershed-scale sediment and TP loads and that storage trends are influenced by channel characteristics and hydraulics. In May 2015, the volume of stored in-channel sediment was estimated within a 13.5 km stretch of Walnut Creek, an alluvial stream draining an agriculturally dominated watershed in Jasper County, Iowa, USA. Storage volume was estimated in-field through a series of 240 transects which were stratified across reaches of the varying channel and hydraulic conditions (e.g., sinuosity, stream power). Overall storage volume was broken down into feature classes (e.g., point bars) based on in-channel depositional processes. Following in-field quantification, feature class sediment samples were collected and analyzed for physical properties (e.g., bulk density) and TP concentration. Physical and chemical analyses, coupled with in-field volume estimation, allowed for watershed-scale masses of in-channel sediment and TP to be calculated and then placed within the context of respective annual loads. Sediment and TP were estimated to be stored at ~2.7 Mg m-1 and 0.7 kg m-1, respectively. Sinuous reaches exhibited significantly greater sediment storage volume (p &amp;lt; 0.001) and depth (p &amp;lt; 0.001) versus straight reaches. Reach sinuosity exhibited a significant positive correlation (p = 0.03) with storage mass and represented the most effective storage predictor. The majority of storage mass (72%) was represented by colluvial material accumulations at the streambank toe. Loose bed sediment was the second greatest contributor to storage mass (18%), with the remaining feature classes (e.g., bars) representing a combined ~10%. Sediment storage mass was ~3.25 times greater than the watershed suspended sediment load for 2015. The TP mass was found to be nearly equal to the respective watershed load for 2015. In-channel sediment and TP storage masses within Walnut Creek were found to be significant in comparison to respective annual loads, and thus storage is expected to play a significant role in respective watershed routing, loading, and the overall budgets of these parameters. Though challenging, quantification of in-channel fine sediment and TP storage is necessary to relate source contributions (e.g., streambank erosion) to watershed loads and is critical to account for interannual sediment and TP export. Keywords: Channel evolution, Channel morphology, Iowa, Sinuosity, Stream power, Water quality, Watershed export.

A novel method for optimizing air temperature estimation and quantifying canopy layer heat island intensity in eastern and central China

Many predictors are considered in estimating the spatial distribution of air temperature. However, a key problem remains the optimal selection of predictors. In this study, genetic algorithm (GA) was used to select optimal regression variables among 17 predictors, and GA-selected predictors were applied to random forest (RF) regression models for mapping air temperature in eastern and central China. By comparison with observed air temperature, results indicate that estimation errors of RF regression models constructed with GA-selected predictors first decrease (up to 5 predictors) and then remain stable. It is found that optimal combination of regression variables has the lowest estimation error (RMSE = 1.21 °C) and the best fitting precision (R2 = 0.9662), including 5 predictors that are latitude, relative humidity, elevation, distance to prefecture city and distance to third-order stream. Next, we compared the quantification of canopy layer heat island intensity (CLHII) based on the analysis of observed and estimated air temperature. We infer that quantification of CLHII using ground monitoring network results in obvious deviation due to the sparse weather stations only providing limited information over wide areas. Finally, we evaluated the robustness in quantifying the CLHII based on estimated air temperature derived from GA-1, -2, -3, -4, -5 and -17 models. Results show that the estimation of air temperature with low estimation error facilitates quantifying accurate CLHII, emphasizing the importance of selecting optimal regression variables. In summary, results reveal the effectiveness of GA in selecting optimal regression variables and provide insight into quantifying CLHII.

Distribution Pattern of Ichthyofaunal Diversity in Different Habitats in the First-, Second- and Third-Order Streams of Randi Gad from Garhwal Himalaya, India

The present study was undertaken to report the ichthyofaunal diversity on spring-fed hill stream Randi Gad from Pauri Garhwal District, Uttarakhand, India. In this work, the author proposed one novel approach, viz. stream order-wise study of distribution and diversity of fish fauna from Garhwal Himalaya, India. A total of 121 fish species including 4, 12 and 22 fish species were collected from first-, second- and third-order streams of Randi Gad. The ichthyofaunal biodiversity observed belonged to 4 families, 10 genera and 22 species. The first-order stream had shown minimum diversity (4 species) and fish productivity of 07CPPs. The second-order stream showed productivity of 24CPPs (12 species). The third-order stream was the most diverse (22 species) and showed fish productivity of 38 CPPs (calculated productivity points system). Thus, the spring-fed hill stream Randi Gad has good potential for fish fauna.

Groundwater–surface water interactions in an ephemeral savanna catchment, Kruger National Park

The semi-arid conditions in savanna landscapes ensure that ephemeral drainage dominates the hydrological network in these dryland systems. Quantification of their hydrological processes is important to inform ecosystem understanding and future conservation efforts under a changing climate, and to provide guidance for restoration. By combining in situ hydrometric observations, hydrochemistry, remote sensing and a soil water balance model, we characterise the groundwater–surface water interactions in ephemeral low-order catchments of the granitoid regions of the southern Kruger National Park (KNP). Streams at the lowest orders are augmented by lateral interflows from the catena, although the second- and third-order stream reaches are conduits for groundwater recharge to the fractured rock aquifer; the soils of the crests and foot-slopes also show preferential flow, and are truly recharge soils, whilst the duplex soils of the midslopes clearly show their responsive nature to a low soil moisture deficit in the shallow horizons. Actual evaporation (aET) differed between catena elements with surprisingly little variation at third-order hillslopes, with the greatest overall aET at the first order. Meanwhile, soil water balances demonstrated a significant variation in storage of the riparian zones as a result of interflow from upslope and aET losses. Furthermore, data support broader-scale observations that groundwater recharge through the vadose zone to the fractured rock aquifer is dependent upon threshold antecedent precipitation conditions. Moderate precipitation events (5 mm/day – 35 mm/day) over a 2–3 week period initiate groundwater responses with a 2–3 month lag, whilst intense precipitation events (100 mm/day) are expressed within 2–3 weeks.Conservation implications: Understanding the lateral connectivity of terrestrial ecosystems to the ephemeral drainage network expressed via hydrological processes in these savanna landscapes is important to infer potential impacts of climate variability on the continued conservation of these ecosystems, both within and external to protected areas.

Hydrogeomorphic assessment of badlands in part of the Mandakini River watershed, Chitrakoot, India

Badlands are a hydrogeomorphological feature with operative processes leading to intense erosion. This study utilizes the morphometric methods with the help of remote sensing data in a GIS environment to determine the characteristics of the badlands of Mandakini River watershed and their interpretation to explore the factors responsible for the formation of the typical landforms. Objective interpretation of morphometric data of badlands with the help of statistical Pearson’s correlation coefficient (PCC) and dendrogram cluster may be made to emphasize the controlling factors. The morphometric parameters like the total number of streams (Nu), bifurcation ratio (Rb), drainage density (Dd), drainage frequency (Fs), drainage texture (Dt), and infiltration number (If) and their correlation in the study area plays a significant role in the advancement of rills and gullies. In the present area, the total number of streams (Nu) is very significantly related with the lengths of the first-order (L1), the second-order (L2), and the third-order streams (L3) along with the total stream length of all orders (Lu) in the third-order and the fourth-order sub-watersheds. Bifurcation ratio (Rb) is strongly correlated with L1, L2, L3, L4, and drainage texture (Dt) in the fourth-order sub-watershed. These correlations insinuate a tectonic influence in the basin and show an ultrafine drainage texture that ultimately forms badland topography. The relation between Dd-Lg-C-If-Rn produces a self-enhancing system of badland development, which promotes erosion in the area under study. These correlations provide a well-figured observation of the sub-watershed that, due to the increase in infiltration number (If), the drainage density (Dd) also increases, which leads to enhancement of channel cutting and erosion rates (low Lg and C value). This correlation coefficient of Rn is moderately low, indicating a single storey type of badlands. The badlands seem to have formed owing to setting up of self-enhancing erosive system on paleo wetlands, as evidenced by the presence of calcretes. Calcretes have been related to the presence of wetlands’ conditions. These have been related to fall in water levels, therefore, indicating much higher water levels nearly close to ground surfaces before setting up badlands conditions. Thus, the badlands which have shallow calcretes horizons can be said to have been wetlands in the past.

Habitat associations and distributions of two endemic crayfishes, Cambarus (Erebicambarus) maculatus Hobbs &amp; Pflieger, 1988 and Faxonius (Billecambarus) harrisonii (Faxon, 1884) (Decapoda: Astacoidea: Cambaridae), in the Meramec River drainage, Missouri, USA

Abstract Understanding the habitat associations and distributions of rare species is important to inform management and policy decisions. Cambarus (Erebicambarus) maculatus Hobbs &amp; Pflieger, 1988, the freckled crayfish, and Faxonius (Billecambarus) harrisonii (Faxon, 1884), the belted crayfish, are two of Missouri’s endemic crayfish species. Both species are listed as Vulnerable (S3) on Missouri’s Species and Communities of Conservation Concern Checklist due to their limited range within the Meramec River drainage (MRD) and the impact of anthropogenic activities therein. Their distributional overlap offers an opportunity for multi-species research to address gaps in information required for conservation. We sampled 140 sites throughout the MRD during the summers of 2017 and 2018 for crayfishes and associated habitat variables, which we related to crayfish presence in an occupancy modeling framework. We found that C. maculatus occupancy was associated with larger stream size, boulder substrate, dolomite lithology, aquatic vegetation beds, dissolved oxygen, and pool mesohabitat. Faxonius harrisonii occupancy increased with boulder substrate, aquatic vegetation beds, the presence of C. maculatus, and decreased in third-order streams. We also expanded the known range for both species within the MRD. Range estimates (watershed area) for C. maculatus and F. harrisonii were 4,347 km2 and 3,690 km2, respectively. This study demonstrates the importance of targeted rather than opportunistic sampling for species distribution.

Urban growth threatens the lowland Amazonian Manaus harlequin frog which represents an evolutionarily significant unit within the genus Atelopus (Amphibia: Anura: Bufonidae)

The Manaus harlequin frog is an evolutionarily significant clade within the Atelopus hoogmoedi species complex. Analyses of 16S and COI concatenated sequences support Atelopus from the Manaus region as an evolutionary significant unit, sister of all species of a Guiana Shield clade. A previous study showed that subtle changes in stream characteristics influence the Manaus harlequin frog occurrence and density variation at local-scale in a reserve on the outskirts of Manaus. As deforestation is approaching areas where the Manaus harlequin frog occurs, we asked how site and landscape heterogeneity influence the geographic boundaries, occurrence patterns, and density variation of the Manaus harlequin frog. We searched for the frog in 80 plots that measured 250 m by 4 m on banks of first- to third-order streams during the rainy seasons in 2012–2013 and 2016–2019. The plot distribution covered all likely areas of occurrence of the Manaus harlequin frog and extended to the areas where it is substituted by its geographically closest relative on the Guiana Shield. Ecological drivers related to climate, flooding events, and forest structure apparently restrict the Manaus harlequin frog to a patchy distribution in a narrow portion of the interfluve between the Negro and Uatuma Rivers. Densities of individuals varied in response to subtle changes in floodplain and stream characteristics. The Manaus harlequin frog is associated with a very specific habitat that is directly affected by the growth of Manaus, the largest city in Amazonia. We conclude that it is endangered and urgent actions are required for its conservation.

Release of dissolved organic matter (DOM) in an autotrophic and productive stream in Pampean region

The aim of our study was to analyze dissolved organic carbon processing at a reach of a productive Pampean stream and to determine DOM retention efficiencies under a wide range of hydrological conditions. This study was carried out in Las Flores stream, a third-order stream located in the Lujan River basin in the northeast of the Buenos Aires province, Argentina. We selected a 2.2 km reach of Las Flores stream. On each sampling occasion, we collected water samples at the end of the reach, at two upstream tributaries, and at the potential hydrological contributors (end members) to stream flow. We determined DOC concentration and DOM optical properties in the stream and end members by combining absorbance–fluorescence spectroscopy techniques. The reach acts as a reactor for DOC concentration at baseflow condition, when in situ production processes prevailed. However, DOC is passively transported downstream at high flow condition. We found that humic and more degraded compounds predominate in DOM at the end of the reach. According to this, we proposed that both protein-like and humic-like compounds are produced at the study reach through in situ production processes, such as biological production from periphyton and macrophytes decomposition.

Assessment of geomorphological and hydrological variations in Bhagirathi River Drainage sub-basin with the help of morphometric studies

ABSTRACTInterpretation of geomorphic features and drainage characteristics of Bhagirathi River sub-basin was carried out with the help of morphometric analysis. Various, areal, linear and relief parameters were calculated to assess drainage basin characteristics quantitatively, determine infiltration and surface runoff behavior control of drainage. The drainage network was analyzed using IRS-PAN satellite data and Survey of India toposheets. Findings show that the Bhagirathi sub-basin from Gaumukh to Chirbas exhibits dendritic to sub-dendritic drainage patterns and is characterized by third-order streams up to Chirbas. Stream segments development in the basin is controlled by local relief and slope. The bifurcation ratio indicate disparity of bifurcation between the different stream orders owing to structural control and circularity ratio indicates sub-elongated shape of basin. This study will be helpful for making soil erosion prevention strategies and its conservation and facilitate the understanding of water retention function in river basins.

Tree roots as a dominant agent of streambed habitat, profile pattern, and grade control

Tree roots are a ubiquitous biotic agent in numerous fluvial settings, but their role in controlling streambed habitat and profile patterns is understudied. Although their importance in resisting bank erosion is more widely reported, tree roots also have the potential to span the channel bed, particularly in narrower first- to third-order streams. This enables tree roots to drive profile patterns and maintain important habitat elements such as steps that induce deep pools in both perennial and ephemeral systems. In a study across two humid-temperate ecoregions, tree roots were associated with more abundant and larger steps than large wood (LW), forming 91% of the steps in the high gravel load setting and 40% of the steps in the steeper, coarser, low sediment supply setting. When combined with LW, a majority of the steps in both settings were formed by biotic agents (97% and 55%, respectively). Furthermore, 70% of the deepest pools across all 40 study reaches were associated with biotic controls, with root steps being the most dominant driver: 45% of the deepest pools in all study reaches, including the maximum pool depths measured in both ecoregions (0.57-m and 0.38-m, respectively). Many questions need further exploration, for example, what tree sizes and species are most likely to form root steps (i.e. trunk diameters > 40 cm and American Sycamore (Platanus occidentalis) in this study); however, even this somewhat limited study has clear implications to land use planning and stormwater management. For example, on land developments draining to root-step dominated streams, maintaining the integrity of the riparian zone would seem to be as important as ensuring hydrologic mimicry if channel integrity is to be preserved. The study also has insights to the stream restoration industry where conventional practice typically involves large tree clearing operations to facilitate stream regrading.

Active bidirectional tectonic-tilting in a part of the Almora Klippe, Kumaun Lesser Himalaya, India: Insights from statistical analyses of geomorphic indices

The NW-SE trending, synformal Almora Klippe in central Kumaun Lesser Himalaya is actively uplifting along the basal thrust, which is known as North Almora Thrust (NAT) and South Almora Thrust (SAT) along the northern and southern flanks, respectively. Geomorphic indices of ‘Basin Asymmetry Factor (AF)’ and ‘Transverse Topography Factor (T)’ of 77 drainage basins of third-order streams developed on this tectonic block have been computed to decipher active tilt-block tectonics of a part of this vast klippe. Statistical analyses of the basins' geomorphic indices revealed differential, gentle to steep, bidirectional tilting of the Almora Klippe vis-à-vis lent insight into correct perspective which these must be used for such studies. The tectonic block of Almora Klippe is partitioned into two minor tectonic blocks along the hinge of the synform. Differential movements along the basal thrust of the klippe have caused westward down-tilting of the northern fold flank (‘AF’ having χ2 value of 7.556 for 4 azimuth classes at 90% confidence level, and ‘T’ having vector mean (θ¯v) of 260° and vector magnitude (r) of 0.25 at p-value of 0.1154), and eastward down-tilting of the southern fold flank (‘AF’ having χ2 value of 13.73 for 4 azimuth classes at 90% confidence level, and ‘T’ having vector mean (θ¯v) of 56° and vector magnitude (r) of 0.26 at p-value of 0.0585). The westward down-tilting of the northern fold flank is due to its faster uplift in the east, along the NAT. Similarly, the eastward down-tilting of the southern fold flank is due to its faster uplift in the west, along the SAT.

Rapid and Stable Microbial Community Assembly in the Headwaters of a Third-Order Stream.

Small streams and their headwaters are key sources of microbial diversity in fluvial systems and serve as an entry point for bacteria from surrounding environments. Community assembly processes occurring in these streams shape downstream population structure and nutrient cycles. To elucidate the development and stability of microbial communities along the length of a first- through third-order stream, fine-scale temporal and spatial sampling regimes were employed along McNutt Creek in Athens, GA, USA. 16S rRNA amplicon libraries were constructed from samples collected on a single day from 19 sites spanning the first 16.76 km of the stream. To provide context for this spatial study and evaluate temporal variability, selected sites at the stream's upper, mid, and lower reaches were sampled daily for 5 days preceding and following the spatial study. In a second study, three sites at and near the creek's headwaters were sampled daily for 11 days to understand initial bacterioplankton community assembly. Both studies revealed decreasing alpha and beta diversity with increasing downstream distance. These trends were accompanied by the enrichment of a small fraction of taxa found at low abundance in headwater-proximal sites. Similar sets of taxa consistently increased in relative abundance in downstream samples over time scales ranging from 1 day to 1 year, many of which belong to clades known to be abundant in freshwater environments. These results underpin the importance of headwaters as the site of rapid in-stream selection that results in the reproducible establishment of a highly stable community of freshwater riverine bacteria.IMPORTANCE Headwater streams are critical introduction points of microbial diversity for larger connecting rivers and play key roles in the establishment of taxa that partake in in-stream nutrient cycling. We examined the microbial community composition of a first- through third-order stream using fine-scale temporal and spatial regimes. Our results show that the bacterioplankton community develops rapidly and predictably from the headwater population with increasing total stream length. Along the length of the stream, the microbial community exhibits substantial diversity loss and enriches repeatedly for select taxa across days and years, although the relative abundances of individual taxa vary over time and space. This repeated enrichment of a stable stream community likely contributes to the stability and flexibility of downstream communities.